Acid treatment of metal articles



Patented Nov. 4, 193 b UNITED STATES Examine PATENT OFFICE RALPH E. LAWRENCE, OF

WICKLHFE, OHIO, ASSIGNOR TO THE GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF DELAWARE ACID TREATMENT OI METAL ARTICLES Io Drawing.

ooon-ou -s-ri,

It forms easily thio st ers for instance, eth ylt hioglycollic' acid the action of chloracetic adid upon sodium sulfid forms ETCldZ -ooon on. -sson.-ooon,

and this latter, in common with most organic compounds having an S atom between E two C atoms, forms polysulfides by addition of sulfur to the S between the carbon atoms; these compounds are characterized by having in common the same radical:

coon-on.-s,

and it seems that this radical is, in this class of substances, the determining factor in developing the inhibiting property. As a matter of fact thio-glycollic acid, its salts and es -,thio-di-glycollic acid, s, etc., poly-thio-glycollic acids and; similar substances containing in their molecule the radical CO OH--GHz-S display to a varying, and in some instances to a very marked degree, the property of inhibiting the action of acids upon metals.

It is at the present'time understood that the action of the inhibitors generally func- 50 tions mainly in relation to the hydrogen ion throughout the bath in a Application filed October 9, 1929. Serial No. 898,505.

of an acid bath and is practically independent of the anion; this is also believed to be true with the novel inhibitors of my present invention, as I found that the thioglycollic acid and its derivatives display ttdieir inhibiiting afitiondwith various non-ox- 1 izing aci s, suc, as ilute sulfuric hydrochloric, acetic etc., acids, solutions of acid sill fates, e c., acid metal cleaning operations.

Various non-oxidizing acids are used in different concentrations and under difierent conditions in metal pickling and cleaning operations. The application of my invention to these operations does not necessitate the composition of any material change in the acid baths therein, except the addition to such baths of small amounts of my inhibitors. As a rule amounts of A; of 1%, or less of a thioglycollic acid or its derivative is suflicient to insure a far going protection of the metal against attack, or corrosion of the metal itself without affecting the dissolution of acid soluble incrustations on the articles. Some of my novel inhibitors are difficulty soluble in the dilute acid baths used and it is therefor necessary to provide for a uniform distribution of the inhibitor finelydivided form. This is easily achieved by adding it in the form of a water soluble salt or mixing it first W such as suIfur1c. Tt isa so p 0 mix thmiibitdr'first with a retest; e colloid and -foaming agent. Whensuch compounded inhibitors are added to the dilute ,acid they will precipitate uniformly and in fine suspension and insure their' nid'sf'figcientaction.

Th-Ffiiciency of inhibitors is conveniently determined by laboratory tests involving the measurement under comparative conditions of the gas evolved from a standard piece of steel immersed in dilute sulfuric acid containing various amounts of the inhibitor.

The results tabulated below have been obtained from pieces of black, mild steel sheet of about 8 square inches Sui famed at room temperature in 34% sulfuric acid and give the amount of gas evolved in cc.

which are commonly used in Amount of inhibitor 0. 0. 1% 0.05%

- I I I I Hours otimmersion 1 2 6.20 1 2 6, 2o Tbioglycollic acid 3063'; 121; aso Ethy -thio'glyco11ic acid. 3 8 3 4 3 7| 20; 80 5 hio-diglyoollic acid 150, 195 850 Poly-thioglycollic acid 34 60, 200 350 Same am dispersed in 00 B. l

sulfuric acid I s 11 40,57

The evolution of gas in a blank test containing no inhibitor was already considerably more than 400 cc. after 6 hours immersion.

claim: 1. In a process of pickling and cleaning metal articles which comprises subjecting said 15 articles to an acid bath containing as the active pickling and cleaning ingredient a nonoxidizing acid, the step of inhibiting the action of said acid upon the metal by the in corporation into said acid of an inhibitor of the class of substances comprising thio-glycollic acid and its derivatives containing the radical COOHCH S.

2. In a process of pickling and cleaning metal articles which comprises subjecting said. articles to an acid bath containing as the active pickling and cleaning ingredient a nonoxidizing acid, the step of inhibiting the action of said acid upon the metal by the incorporation into said acid of an inhibitor of the class of substances comprising thio-glycollic acid and its derivatives containing the radical GOOHCH S finely dispersed throughout said bath.

A composition of matter for pickling and cleaning metal articles comprising a dian inhibitor of the class of substances comprising thio-glycollic acid and its derivatives containing the radical COOH-CH S.

4. A composition of matter for pickling and cleaning metal articles comprising a dilute non-oxidizing acid and a small amount of an inhibitor of the class of substances comprising thio-glycollic acid and its derivatives containing the radical COOHCH finelydispersed throughout said acid.

In testimony whereof, I afiix my si ature.

RALPH E. LAWRE CE. 

